Simple question(s) that needs an answer (1 Viewer)

[underthesun]

First question

In volume problems, do you have to write the Riemann sum thingy with Delta X and that lim n->infinity and stuff in HSC exam situations?

Second Question

What is kg wT? My maths teacher says 1 kg wT = 9.8 N. This is a problem on circular motion.

Third Question

This question is a physics question, but of course, maths extension 2 students are of higher quality , and hence asking from you guys should give a more accurate result. (no offense to them physics students )

1. You buy a sanyo weight scale, designed for earth.

2. You bring it to moon.

3. The scale reads 40 kg as you stand on it.

Assuming that that the gravitational acceleration on objects on the moon surface is 6 times less, what is your mass?

(i'd say 240 kg, but my physics teacher is saying it remains 40kg)....

*edited for clarity

 

[ND]

What is kg wT? My maths teacher says 1 kg wT = 9.8 N. This is a problem on circular motion.

No idea what kg wT is, but the eqn looks similar to F=ma (with a=g). Maybe OLDMAN with his BSc can answer you.

This question is a physics question, but of course, maths extension 2 students are of higher quality , and hence asking from you guys should give a more accurate result. (no offense to them physics students )

1. You buy a sanyo weight scale, designed for earth.

2. You bring it to moon.

3. The scale reads 40 kg as you stand on it.

Assuming that that the gravitational acceleration on objects on the moon surface is 6 times less, what is your mass?

(i'd say 240 kg, but my physics teacher is saying it remains 40kg)....

The weight would definately change. F=ma, so when a is different, F is different. This is about the Q in the CSSA paper right? That question asked about mass, but a scale actually reads weight (but presents it as mass), so the scale would read differently on mars. His mass however, would remain the same.

 

[underthesun]

Yeah, because my maths teacher says he is very sure about that kg wT or stuff thing.

bout that CSSA stuff, yep it is .

 

[OLDMAN]

Your teacher is right. There is a distinction between 1 kg mass and 1 kg wt. The later is a force equivalent to 1*9.8 =9.8 Newtons. Thus if a force of 1 kg wt is applied to a mass of 1 kg, an acceleration of 9.8 m/s^2 results.

 

[freaking_out]

Originally posted by OLDMAN
Your teacher is right. There is a distinction between 1 kg mass and 1 kg wt. The later is a force equivalent to 1*9.8 =9.8 Newtons. Thus if a force of 1 kg wt is applied to a mass of 1 kg, an acceleration of 9.8 m/s^2 results.

yeah, kg wt is just another way of expressing force...and to get it in terms of newtons, just times it by g.

btw...underthesun...i thought u've already sat for the 4u hsc last year?

 

[underthesun]

Originally posted by freaking_out
btw...underthesun...i thought u've already sat for the 4u hsc last year?

I have, but the internal assessment mark was so botched, I deserved it because of bludging. Hence, I'm repeating. Good thing i was accelerated, so the shame of repeating is less than half.

Imagine repeating full year! I'd have to move school for that


Can someone confirm the third questions? There are someone at my school who still doesn't believe me even after a 45 minute argument, and when I mentioned bos.org he says he is starting to doubt bos.org forums..

i am not making a propaganda

 

[freaking_out]

Originally posted by underthesun
I have, but the internal assessment mark was so botched, I deserved it because of bludging. Hence, I'm repeating. Good thing i was accelerated, so the shame of repeating is less than half.

Imagine repeating full year! I'd have to move school for that


Can someone confirm the third questions? There are someone at my school who still doesn't believe me even after a 45 minute argument, and when I mentioned bos.org he says he is starting to doubt bos.org forums..

i am not making a propaganda

I think the misunderstanding arises from the fact that some people think laterally/practically about the scale and say that it measures weight and it reads out the mass....whilst other simple minded people (like the examiners)take it that scales just measure your mass, fullstop.

so i reckon it really depends on how u look at it... me personally if i was in an exam would say 40kg, coz i wouldn't be bothered arguing about the teacher about how earthly scales really measure weight and give u a mass reading etc.

oh yeah, abt. repeating, theres this guy in my school repeating all of his subjects in the same school....man thats courage.

 

[underthesun]

But those simple minded people forgot that weights can't measure your mass in the moon / mars, since it was designed for the earth.

Repeating in the same school? That's very brave actually..

 

[freaking_out]

Originally posted by underthesun
But those simple minded people forgot that weights can't measure your mass in the moon / mars, since it was designed for the earth.

Repeating in the same school? That's very brave actually..

yeah, well thats what happens when examiners try to make their questions sound realistic....but remember the new syllabus expects us to not use common sense...u just have to know whats in the syllabus no more no less.

oh yeah...its very brave indeed, repeating all of year 12 in the same skool...

 

[maniacguy]

I believe the examiners work off the principle that the scales measure weight, then divide by 9.8 to give you your actual mass. Ergo, mass remains constant.

 

[freaking_out]

Originally posted by maniacguy
I believe the examiners work off the principle that the scales measure weight, then divide by 9.8 to give you your actual mass. Ergo, mass remains constant.

hey, btw what did the official answers say?

 

[underthesun]

40kg. I typed up proof that should disprove beyond doubt that 40kg is wrong anyways

Maniac can speak elloquently there

 

[underthesun]

Originally posted by balekrision
Kg is the SI unit for MASS, make sure you don't get the two mixed up.
A person's mass will not change, only the force exerted by gravity on that mass changes, because of the acceleration.
Less acceleration on the moon therefore the moon applies a smaller force on your mass. A scale COULD have an inbuilt sensor to detect acceleration, and I believe they do (otherwise they wouldn't work for different places ON Earth), by having an small mass inside they could measure the force exerted on that mass and determine the acceleration due to gravity since they KNOW that mass. Using that determined acceleration they could calculate your mass.

nope, scales display in kg wT.

Because the question says specifically that it is calibrated for the earth or designed for earth, then even if they have an inbuilt acceleration sensor, they would perform as if they are on the earth.

 

[freaking_out]

Originally posted by underthesun
nope, scales display in kg wT.

Because the question says specifically that it is calibrated for the earth or designed for earth, then even if they have an inbuilt acceleration sensor, they would perform as if they are on the earth.

whats kg WT again??? i've seen it in fitzpatrick but never quite understood it...

 

[underthesun]

1 kg wT = 9.8 N, it's just another unit of force.

now because scales display "kg", and they're really measuring force, it means that they must be measuring the force in kg wT...

 

[Constip8edSkunk]

unless its 1 of those balancing scales

 

[freaking_out]

Originally posted by underthesun
1 kg wT = 9.8 N, it's just another unit of force.

now because scales display "kg", and they're really measuring force, it means that they must be measuring the force in kg wT...

hmm... so whats the diff. b/w that and the mass unit kg?

 

[turtle_2468]

Okay. I'll take on Qs 1 and 3.
Q1: Probably. I'd do it in 1 line just to make sure I don't get docked a mark, although they _might_ be nicely inclined and give u full marks if u get answer right...
Q3: 240kg.
Your MASS is the same on the moon and on the earth. But that's not the point! The scale measures WEIGHT, and then "converts" that to mass for u. That is because your force upon the scale is what forces the needle to move.
example: It's because you put ~500N on the scale at home that the scale reads 50 kg.

Now... suppose you bring the scale to the moon. Then as the scale reads 40kg, it means that it has the same force on it that 40kg on earth would produce = 40*9.8~400. HOWEVER, that means that 400 newtons is the force applied by you on the scale. Therefore (9.8/6)*mass=400, and so mass=240 kg.

The difference is that kg wT is a measure of FORCE. kg is a measure of MASS. If you stood under a car, it'd still weight 3000 kg but it would apply 3000 kg wT to your head, probably crushing it beyond repair. (unless you're in v low gravity or something..)

 

[underthesun]

Originally posted by turtle_2468
Okay. I'll take on Qs 1 and 3.
Q1: Probably. I'd do it in 1 line just to make sure I don't get docked a mark, although they _might_ be nicely inclined and give u full marks if u get answer right...
Q3: 240kg.
Your MASS is the same on the moon and on the earth. But that's not the point! The scale measures WEIGHT, and then "converts" that to mass for u. That is because your force upon the scale is what forces the needle to move.
example: It's because you put ~500N on the scale at home that the scale reads 50 kg.

Now... suppose you bring the scale to the moon. Then as the scale reads 40kg, it means that it has the same force on it that 40kg on earth would produce = 40*9.8~400. HOWEVER, that means that 400 newtons is the force applied by you on the scale. Therefore (9.8/6)*mass=400, and so mass=240 kg.

The difference is that kg wT is a measure of FORCE. kg is a measure of MASS. If you stood under a car, it'd still weight 3000 kg but it would apply 3000 kg wT to your head, probably crushing it beyond repair. (unless you're in v low gravity or something..)

Problem is, my maths teacher emphasizes to write 3 lines or something of the riemann sum stuff. Oh well, better be safe than sorry..

Great, now the answer to number 3 came from the person It should have come from

 

[freaking_out]

Originally posted by underthesun
Problem is, my maths teacher emphasizes to write 3 lines or something of the riemann sum stuff. Oh well, better be safe than sorry..

Great, now the answer to number 3 came from the person It should have come from

what the heck is riemann sum??? i've never heard of that either.